Use pybind11 in _c_internal_utils module

[QuLogic]

PR summary

I changed to a C++ file, in order to use pybind11, though I'm not sure if the name should change. I also made the HWND into a capsule so we could check types a bit more stringently, though this is assuming no-one ever wants to call SetForegroundWindow with a handle obtained elsewhere.

This depends on the Meson PR, as it was much easier to iterate with its automatic re-compile in editable installs.

PR checklist

• [n/a] "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• [n/a] Plotting related features are demonstrated in an example
• [n/a] New Features and API Changes are noted with a directive and release note
• [n/a] Documentation complies with general and docstring guidelines

[tacaswell]

I think changing to a capsule is a good idea (maybe we want an API change note?).

I lean to leaving the name. Even though it is cpp, Python still calls them "C-extensions" so being a bit imprecise and leaving the name as _c_internal_utils seems fine.

[QuLogic]

I think changing to a capsule is a good idea (maybe we want an API change note?).

It is private at least, so no need?

[ianthomas23]

I'd be inclined to remove the 4 uses of void in function argument lists now that these functions are C++ rather than C, but I don't feel strongly about this.

[oscargus]

Let's merge this and the voids can possibly be handled later.